A vehicle condition detection device is produced such that a detecting element for acceleration, angular velocity or the like, for example, is resin molded, and used as, for example, a sensor for an airbag device or an attitude control device of an automobile. Vehicle condition detection devices are disposed as shown in FIG. 12, for example, in the case of the airbag device. To be more specific, vehicle condition detection devices 2, 5 are arranged in an engine room of a vehicle 1, a vehicle condition detection device 8 is disposed under a sheet, vehicle condition detection devices 3, 4, 6, 7 are disposed within pillars, and a vehicle condition detection device 9 is arranged in a trunk room. At the time of collision, a condition detection signal is sent to an air bag controller 10, and thereby an airbag (not shown) is instantaneously blown up to protect an occupant. As mentioned above, since the vehicle condition detection device occupies a small space, and is disposed in a plurality of places, it is required that the device be small in size, lightweight, and low-priced. On the other hand, since the vehicle condition detection device affects vehicle safety, it is desired to have uniform product stability and further be able to maintain a high precision performance under severe environments for a long term, which is known as high reliability.
A structure of a conventional vehicle condition detection device, and molding molds thereof are shown in FIG. 13. A detecting element 11 for detecting the condition of a vehicle is mounted on a lead frame 18, and a molding process is implemented therearound with a resin to form a primarily molded body 12. A lead terminal 14 of the detecting element 11 formed by the lead frame 18 is extended from the primarily molded body 12. The primarily molded body 12 is subjected to a secondary process to shape the detecting element 11 as a connector for wiring and add thereto a structure secured to a vehicle. First, the lead terminal 14 is welded to a connector terminal 16 for connecting the lead terminal to an external harness. Then, in order to form a connector housing and a fastening portion, the primarily molded body 12 is held in a predetermined space between an upper mold 119′ and a lower mold 120′, and a resin is injected into a space between the two molds and the primarily molded body 12 to mold a secondarily molded body 13. When the secondary molding process is carried out, the primarily molded body 12 having the detecting element 11 located therein is sandwiched between convex primarily-molded-body-holding portions 28, 28, which are provided in the upper mold 119′ and the lower mold 120′, respectively, and are opposed to each other, to be held, and also restrain the application of a thermal stress on the detecting element 11 upon a resin injection. Further, the connector terminal 16 is inserted into a sliding mold 121′ and held therein. In the case of the above method, a portion of the secondarily molded body 13 serving as a casing of a vehicle condition detection device, in other words, a trace caused by pulling-out of the primarily-molded-body-holding portions 28, 28 is formed by a vertical hole 29 that communicates from the outside to the face of the primarily molded body 12, as shown in FIG. 13(b) and FIG. 13(c).
Moreover, Patent Document 1 discloses a technique by which an air-tight type detecting element structure and a signal processing circuit of an acceleration sensor are fixed on a lead frame; a wire bonding between the detecting element structure, the signal processing circuit, and the lead frame is carried out; thereafter, the resultant is completely molded therearound with a plastic material; and at that time, a thermal stress relaxation mechanism is arranged to be provided in the detecting element structure or a plastic structure enclosing the detecting element structure such that the deformation of the detecting element structure itself that is caused by the thermal stress due to a difference in thermal expansion coefficient between the detecting element structure and the plastic material is minimized. The technology aims at producing a low cost, small-sized, and lightweight acceleration sensor by a mounting method of performing a full-mold process. Further, it is said that the arrangement of the thermal stress relaxation mechanism can minimize the deformation of the detecting element structure itself to thereby improve the temperature characteristic of the acceleration sensor.